1. Field of the Invention
The present invention relates to apparatus and methods for combining laser beams. The present invention further relates to apparatus and methods employing combined laser beams, such as color laser beam displays and laser beam modulators for fiber optic data transmission.
2. Description of the Prior Art and Related Information
In a variety of applications, it is necessary or advantageous to combine laser beams into a single beam. For example, in a color laser beam display, it is advantageous to combine different color laser beams into a single beam which is then scanned over the display screen. While it is of course possible to combine two or more laser beams at a particular spot simply by directing the beams to converge there, such an approach to combining laser beams is unsuitable if the combined beam itself needs to be scanned. This is the case since the beams will immediately begin to diverge after leaving the spot at which they are brought together. Therefore, if the resulting combined beam is directed down an optical path of any length, the resulting beam diameter will diverge to an unacceptable degree. For example, in a laser beam display such a combined beam resulting from multiple lasers being focused at a single point on the scanning mirror will diverge to an unacceptable degree before contacting the display screen. Alternatively, if the multiple beams are combined at the display screen then separate optical paths and scanning mechanisms are required for each laser beam. This not only introduces space and cost problems but also introduces alignment and reliability issues due to the difficulty of accurately registering multiple beams along multiple optical paths at a moving target point. Therefore, this approach to combining laser beams is also undesirable. Therefore, most applications requiring mixing of laser beams require the capability for producing a combined beam which does not diverge and can be accurately scanned or otherwise optically steered.
In conventional approaches to combining laser beams together into a single beam which does not diverge, a problem arises in that significant losses in the total beam power are experienced. These losses are a direct result of the need to incorporate optical elements which introduce beam losses, such as beam splitters, dichroic mirrors, or filters, in order to combine the multiple laser beams into a single beam.
Referring to FIG. 1, such a prior art laser beam combining apparatus is illustrated in a color laser beam application. The apparatus of FIG. 1 combines red, blue and green laser beams provided from red, blue and green lasers 1, 2, and 3, respectively, so as to provide a multi-color output beam 4. The red and blue laser beams are combined via a first optical element 5, such as a beam splitter or dichroic mirror. As shown, however, this optical element inevitably introduces a loss of beam energy shown by the beam 6 reflected from the front surface of the optical element 5. Similarly, a second optical element 7 is employed to combine the red and blue beams with the green laser beam and this is also accompanied by a loss shown by reflected beam 8. This lost beam energy, represented by beams 6 and 8 in FIG. 1, can constitute a significant portion of the total available energy. For example, beam losses comprising about 35% of the total power of the red laser 1, 25% of the total power of the blue laser 2 and 15% of the total power of the green laser 3 will be experienced in a color laser mixing scheme such as illustrated in FIG. 1.
The above-noted problem of loss of beam energy due to the mixing of the laser beams is exacerbated by the price differentials for available lasers of different power outputs. Typically, increasing the power of a given laser will dramatically increase the cost of the laser. For example, doubling the output power of the laser may require a different type of laser, e.g., a gas laser as opposed to a semiconductor laser, causing the cost to far more than double. Therefore, when losses due to the mixing reduce the brightness of the combined beams to the point where they no longer satisfy the needs of a particular application, the resulting cost increase can be very significant. In some cases, the cost increases introduced by the deficiencies of the laser beam mixing can render a laser based system uncompetitive in the commercial marketplace. Also, higher power lasers are typically bulkier, using additional space which is undesirable in many applications.
The inherent losses of a laser beam mixing system such as shown in FIG. 1 have also rendered it impractical to obtain high power laser beams by simply mixing together multiple lower energy beams of a given frequency or color. As noted above, high power lasers may be quite expensive and as a result, it would be desirable from a cost standpoint to combine several lower cost, lower power lasers to achieve a given power output rather than use a single more expensive high power laser. Due to the high percentage of loss experienced by the beam mixing, however, it quickly becomes impractical to use multiple stages of mixing of laser beams to form such a higher output beam. For this reason, multi-beam mixing systems as sources of higher powered laser beams have not been widely employed in commercial applications.
In view of the foregoing, it will be appreciated that a need presently exists for an efficient way of combining laser beams, such as for color laser beam applications or for creation of higher power output lasers. Furthermore, a need presently exists for a way to combine plural laser beams in an efficient manner which also allows the resulting combined beam to be easily and precisely scanned or otherwise optically steered.